This invention relates to the treatment of carbon-containing materials. In one aspect this invention relates to the treatment of carbon-containing materials, such as coal, coke and hydrocarbons to produce oxides of carbon therefrom. In still another aspect this invention relates to a process for the production of high purity synthesis gas, a mixture of hydrogen and carbon monoxide, from carbon-containing materials.
Coal and coke may be treated with oxygen and/or steam at relatively high temperatures to convert the coal or coke to hydrogen and carbon monoxide, which products are useful for various purposes including the synthesis of organic compounds therefrom. When steam is used alone to gasify coal or coke it is necessary to supply heat from an external source. The heat released by gasifying coal with relatively pure oxygen tends to be excessive. As the result, steam and oxygen are normally used together in such proportions that the net reaction heat is sufficient to maintain the desired temperatures for the gasification of the coal or coke. In using the combination of steam and oxygen in the above manner the oxygen may be used in a substantially pure form and by such method the process is continuous, thermally efficient, and produces a gas comprising hydrogen and carbon monoxide.
The use of oxygen is an economic burden and increases process complexity. If the oxygen is to be supplied to the process as air rather than as purified oxygen, the economic advantage obtained by using air is obviated by the fact that product gas contains large amounts of diluent nitrogen. It is desirable, therefore, to provide a process which eliminates purification of the oxygen but produces a gas substantially free from nitrogen.
U.S. Pat. No. 2,602,809 discloses the gasification of solid carbon-containing materials using metal oxides, such as Fe.sub.3 O.sub.4 or Fe.sub.2 O.sub.3, which serve as the principal source of oxygen for the reaction. The process disclosed employs a counter-current flow of coal and metal oxide in a fluidized state in a reactor for effecting reduction of the metal oxide to release oxygen and effecting oxidation of the coal with the released oxygen to form carbon oxides. The reduced metal oxide is reoxidized for reuse with air whereby it is heated by the heat from the exothermic air oxidation reaction. If a synthesis gas product is desired, a portion of the reduced metal oxide is reoxidized with steam at an elevated temperature to produce hydrogen. This hydrogen is then mixed with the carbon monoxide obtained from the coal gasification to produce the synthesis gas.